Protection film

ABSTRACT

The present invention provides a protection film including a substrate composed of a polylactic acid film or sheet having tear strength so as not to break or tear during production or processing of the protection film. The protection film according to the present invention is a protection film including a substrate and a removable pressure-sensitive adhesive layer on at least one surface of the substrate, wherein the substrate is composed of a polylactic acid film or sheet comprising polylactic acid (A) wherein the tear strength is not less than 100 N/mm when the film or sheet is torn at least in a flow direction (MD), a rate of dimensional change due to heating is not more than ±3% in the flow direction (MD) and in a transverse direction (TD), and a rate of dimensional change due to loaded heating is not more than ±3% in the flow direction (MD).

TECHNICAL FIELD

The present invention relates to a protection film (including a sheet),and more specifically relates to a protection film including a substratecomposed of a polylactic acid film or sheet that has high heatresistance and high tear resistance, and does not break or tear duringproduction or processing. The protection film can be used, for example,as protection film for protecting the surfaces of wheels of vehicles; asa protection film for protecting the surfaces of optical members andelectronic parts used in liquid crystal displays and the like such aspolarizing plates, wavelength plates, retardation plates, and reflectivesheets; and as a protection film for protecting the surfaces of metalliclayers or metal oxide layers used in electromagnetic wave shieldingmaterials and the like used in plasma display panels and CRTs. Theprotection film is removed by peeling when the film is no longer needed.

BACKGROUND ART

Polylactic acid is a plant-derived biomass polymer, and has beenreceiving attention as a resin alternative to petroleum-derivedpolymers. Polylactic acid, which is a highly elastic and strong polymer,unfortunately, lacks toughness and has low impact resistance, low tearresistance, and low flexibility. Polylactic acid has a low rate ofcrystallization, and barely shows crystal growth in ordinary crystalgrowth. Although the melting point is approximately 170° C., polylacticacid thermally deforms at temperatures of not less than the glasstransition temperature, i.e., not less than 60° C., and cannot keep afilm shape. Then, to improve the heat resistance of polylactic acidresin films, several methods have been heretofore suggested.

As the measures against these problems, a method of blending polylacticacid with a soft and heat resistant polymer to improve the heatresistance of a polylactic acid resin film has been suggested (PTL 1).Alternatively, a method of adding aliphatic polyester/core-shell typerubber to polylactic acid, and monoaxially or biaxially drawing a filmformed of the prepared polylactic acid has been suggested (PTL 2). Bothmethods can attain impact resistance and heat resistance at the sametime. Unfortunately, blending of large amounts of the petroleum-derivedpolymer and additives significantly reduces the ratio of theplant-derived component (degree of biomass).

A technique of giving flexibility and heat resistance to a polylacticacid film has been suggested, in which crystallization of a resincomposition comprising polylactic acid, a plasticizer, and a nucleatoris promoted in a heat treatment step subsequent to a step of molding afilm (PTL 3). Unfortunately, in this method, addition of the plasticizermay cause bleed-out, and an effect of improving tear resistance islittle while an effect of improving flexibility is attained.

CITATION LIST Patent Literature

PTL 1: Japanese Patent Laid-Open No. 2006-70224

PTL 2: Japanese Patent Laid-Open No. 2009-173715

PTL 3: Japanese Patent No. 4699180

SUMMARY OF INVENTION Technical Problem

Then, an object of the present invention is to provide a protection filmincluding a substrate composed of a polylactic acid film or sheet havingtear strength so as not to break or tear during, for example, productionor processing of the protection film or winding thereof into a roll, andcausing neither melt nor deformation at high temperatures more than 100°C.

Solution to Problem

The present inventors, who have conducted extensive research to attainthe above objects, found that the problems above can be solved by useof, as a substrate, a polylactic acid resin film or sheet having a tearstrength of not less than a predetermined value and having a rate ofdimensional change due to heating (%) of not more than a predeterminedvalue and a rate of dimensional change due to loaded heating (%) of notmore than a predetermined value, and have completed the presentinvention.

Namely, the present invention provides

a protection film comprising a substrate and a removablepressure-sensitive adhesive layer on at least one surface of thesubstrate,

wherein the substrate is composed of a polylactic acid film or sheetcomprising

polylactic acid (A),

wherein a tear strength (according to JIS K7128-3: Plastics—Film andSheeting—Determination of Tear Resistance, Part 3: Right angled tearmethod) of the film or sheet is not less than 100 N/mm when the film orsheet is torn at least in a flow direction (machine direction: MD),

the film or sheet stored under an atmosphere at 100° C. for 1 minute hasa rate of dimensional change due to heating of not more than ±3% in theflow direction (MD) and a transverse direction (TD), the rate ofdimensional change due to heating being determined by Expression (1):

rate of dimensional change due to heating (%)=(L2 −L1)/L1×100  (1)

where L1 represents a gauge length before a test, and L2 represents agauge length after the test, and

the film or sheet stored under an atmosphere at 100° C. for 1 minutewhile a load of 300 g/mm² is applied in the flow direction (MD) has arate of dimensional change due to loaded heating of not more than ±3% inthe flow direction (MD), the rate of dimensional change due to loadedheating being determined by Expression (2):

rate of dimensional change due to loaded heating (%)=(L4−L3)/L3×100  (2)

where L3 represents a gauge length before a test, and L4 represents agauge length after the test.

The polylactic acid film or sheet included in the substrate may furthercomprise a reforming agent (E). The polylactic acid film or sheetincluded in the substrate may comprise a polyglycerol fatty acid esterand/or polyglycerol condensed hydroxy fatty acid ester (a) as thereforming agent (E) such that the weight ratio of the polylactic acid(A) to the polyglycerol fatty acid ester and/or polyglycerol condensedhydroxy fatty acid ester (a) is 99:1 to 80:20 ((A):total amount of (a)).

The polylactic acid film or sheet included in the substrate may comprisea core-shell-structured polymer (b) composed of a particulate rubber anda graft layer formed on the outside of the rubber as the reforming agent(E) such that the weight ratio of the polylactic acid (A) to thecore-shell-structured polymer (b) composed of a particulate rubber and agraft layer formed on the outside of the rubber is 99:1 to 80:20((A):(b)).

The polylactic acid film or sheet included in the substrate may comprisea soft aliphatic polyester (c) as the reforming agent (E) such that theweight ratio of the polylactic acid (A) to the soft aliphatic polyester(c) is 95:5 to 60:40 ((A):(c)).

The polylactic acid film or sheet included in the substrate may furthercomprise 0.1 to 10 parts by weight of an acidic functionalgroup-modified olefin polymer (B) based on 100 parts by weight of thepolylactic acid (A) (or a composition comprising the polylactic acid (A)and the reforming agent (E) when the reforming agent (E) is contained),the acidic functional group-modified olefin polymer (B) having an acidvalue of 10 to 70 mgKOH/g and a weight average molecular weight of 10000to 80000. The acidic functional group of the acidic functionalgroup-modified olefin polymer (B) may be an acid anhydride group.

The polylactic acid film or sheet included in the substrate may furthercomprise 0.5 to 15 parts by weight of a fluorine-containing polymer (C)based on 100 parts by weight of the polylactic acid (A) (or acomposition comprising the polylactic acid (A) and the reforming agent(E) when the reforming agent (E) is contained). The fluorine-containingpolymer (C) may be a tetrafluoroethylene polymer.

The polylactic acid film or sheet included in the substrate may furthercomprise 0.1 to 15 parts by weight of a crystallization promoter (D)based on 100 parts by weight of the polylactic acid (A) (or acomposition comprising the polylactic acid (A) and the reforming agent(E) when the reforming agent (E) is contained).

The polylactic acid film or sheet included in the substrate may be afilm or sheet formed by a melt film forming method such as calendering.

The present invention provides

a method of producing a protection film comprising a substrate composedof a polylactic acid film or sheet prepared by forming a resincomposition comprising polylactic acid (A) into a film by a melt filmforming method, the method comprising:

a melt film forming step of melt forming the resin composition,

a cooling solidifying step of cooling and solidifying the resincomposition after the melt film forming step to prepare a film or sheet,and

a crystallization promoting step of heating the film or sheet after thecooling solidifying step to promote crystallization of the film orsheet,

wherein a resin temperature in the melt film forming step is within therange of (Tm) −15° C. to (Tm) +15° C. where Tm represents a meltingtemperature of the resin composition during raising of temperature, and

in at least part of the crystallization promoting step, crystallizationof the film or sheet is promoted within the temperature range of (Tc)+10° C. to (Tc) +50° C. where Tc represents a crystallizationtemperature of the resin composition during the raising of temperature.

The method of producing a protection film may comprise

a residual stress relaxing step after the melt film forming step andbefore the cooling solidifying step,

wherein in the residual stress relaxing step, the resin composition maybe kept within the temperature range of (Tm) −70° C. to (Tm) −20° C.

The resin composition may further comprise a reforming agent (E).

The resin composition may comprise polyglycerol fatty acid ester and/orpolyglycerol condensed hydroxy fatty acid ester (a) as the reformingagent (E) such that the weight ratio of the polylactic acid (A) to thepolyglycerol fatty acid ester and/or polyglycerol condensed hydroxyfatty acid ester (a) is 99:1 to 80:20 ((A):total amount of (a)).

The resin composition may comprise a core-shell-structured polymer (b)composed of a particulate rubber and a graft layer formed on the outsideof the rubber as the reforming agent (E) such that the weight ratio ofthe polylactic acid (A) to the core-shell-structured polymer (b)composed of a particulate rubber and a graft layer formed on the outsideof the rubber is 99:1 to 80:20 ((A):(b)).

The resin composition may comprise a soft aliphatic polyester (c) as thereforming agent (E) such that the weight ratio of the polylactic acid(A) to the soft aliphatic polyester (c) is 95:5 to 60:40 ((A):(c)).

The resin composition may further comprise 0.1 to 10 parts by weight ofan acidic functional group-modified olefin polymer (B) based on 100parts by weight of the polylactic acid (A) (or a composition comprisingthe polylactic acid (A) and the reforming agent (E) when the reformingagent (E) is contained), the acidic functional group-modified olefinpolymer (B) having an acid value of 10 to 70 mgKOH/g and a weightaverage molecular weight of 10000 to 80000. The acidic functional groupof the acidic functional group-modified olefin polymer (B) may be anacid anhydride group.

The resin composition may further comprise 0.5 to 15 parts by weight ofa fluorine-containing polymer (C) based on 100 parts by weight of thepolylactic acid (A) (or a composition comprising the polylactic acid (A)and the reforming agent (E) when the reforming agent (E) is contained).The fluorine-containing polymer (C) may be a tetrafluoroethylenepolymer.

The resin composition may further comprise 0.1 to 15 parts by weight ofa crystallization promoter (D) based on 100 parts by weight of thepolylactic acid (A) (or a composition comprising the polylactic acid (A)and the reforming agent (E) when the reforming agent (E) is contained).

The melt film forming method may be calendering.

Advantageous Effects of Invention

The substrate for the protection film according to the present inventiondoes not melt or deform at high temperatures more than 100° C. Thesubstrate keeps its intrinsic rigidity and does not break or tear whentension is applied to the substrate during, for example, production orprocessing of the protection film or winding thereof into a roll.Furthermore, the protection film according to the present invention doesnot break or tear when the protection film is re-attached in use or isfinally peeled.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view of an example of a calendering film formingmachine used in production of a substrate (polylactic acid film orsheet) for the protection film according to the present invention.

FIG. 2 is a schematic view showing an example of a polishing filmforming machine used in production of the substrate (polylactic acidfilm or sheet) for the protection film according to the presentinvention.

DESCRIPTION OF EMBODIMENTS Substrate

The polylactic acid film or sheet used as a substrate for the protectionfilm according to the present invention is a resin film or sheetcomprising polylactic acid (A). The raw material monomer for polylacticacid, lactic acid, has asymmetric carbon atoms, and has optical isomersof L-form and D-form. Polylactic acid (A) used in the present inventionis a polymer including L-form lactic acid as the main component. As asmaller content of D-form lactic acid is mixed as impurities duringproduction, the resultant polymer has higher crystallinity and a highermelting point. A raw material having high purity of L-form is preferablyused, and those having a purity of L-form of not less than 95% are morepreferably used. Polylactic acid (A) may contain other copolymerizationcomponents in addition to lactic acid.

Examples of the other copolymerization components include polyolcompounds such as ethylene glycol, propylene glycol, 1,3-propanediol,butanediol, pentanediol, neopentyl glycol, hexanediol, heptanediol,octanediol, nonanediol, decanediol, 1,4-cyclohexanedimethanol, glycerol,pentaerythritol, polyethylene glycol, polypropylene glycol,polytetramethylene glycol, and bisphenol A; polyvalent carboxylic acidssuch as oxalic acid, malonic acid, glutaric acid, adipic acid, sebacicacid, azelaic acid, dodecanedione acid, cyclohexanedicarboxylic acid,terephthalic acid, isophthalic acid, phthalic acid,naphthalenedicarboxylic acid, bis(p-carboxyphenyl)methane,anthracenedicarboxylic acid, 4,4′-diphenyletherdicarboxylic acid,5-sodiumsulfoisophthalic acid, and 5-tetrabutylphosphoniumisophthalicacid; hydroxycarboxylic acids such as glycolic acid, hydroxypropionicacid, hydroxybutyric acid, hydroxyvaleric acid, hydroxycaproic acid, andhydroxybenzoic acid; and lactones such as propiolactone, valerolactone,caprolactone, undecalactone, and 1,5-oxepan-2-one. Thesecopolymerization components are contained in a proportion of preferably0 to 30 mol %, more preferably 0 to 10 mol % based on the total monomercomponents that form the polylactic acid (A).

The weight average molecular weight of the polylactic acid (A) is, forexample, 10000 to 400000, preferably 50000 to 300000, more preferably80000 to 200000. The melt flow rate [JIS K-7210 (test condition 4)] ofthe polylactic acid (A) at 190° C. and a load of 21.2 N is, for example,0.1 to 50 g/10 min, preferably 0.2 to 20 g/10 min, more preferably 0.5to 10 g/10 min, particularly preferably 1 to 7 g/10 min. An excessivelyhigh value of the melt flow rate may reduce the mechanical propertiesand heat resistance of the prepared film or sheet. An excessively lowvalue of the melt flow rate may excessively increase load during filmformation.

In the present invention, the “weight average molecular weight” refersto the value measured by gel permeation chromatography (GPC) (in termsof polystyrene). The measurement conditions for GPC are as follows:

column: TSKgel SuperHZM-H/HZ2000/HZ1000

column size: 4.6 mmI.D.×150 mm

eluent: chloroform

flow rate: 0.3 ml/min

detector: RI

column temperature: 40° C.

amount of injection: 10 μl

Polylactic acid can be prepared by any method. Representative examplesof the production method include lactidation and direct polymerization.Lactidation is a method for preparing high molecular weight polylacticacid in which lactic acid is heated and dehydration condensed to preparelow molecular weight polylactic acid; the low molecular weightpolylactic acid is pyrolyzed under reduced pressure to prepare a cyclicdimer of lactic acid, lactide; and the lactide is subjected toring-opening polymerization in the presence of a metal salt catalystsuch as tin(II) octanoate. Direct polymerization is a method fordirectly preparing polylactic acid in which lactic acid is heated in asolvent such as diphenyl ether under reduced pressure to be polymerizedwhile the moisture content is being removed to suppress hydrolysis.

Commercially available products can be used as the polylactic acid (A).Examples of commercially available products include trade names “LACEAH-400” and “LACEA H-100” (made by Mitsui Chemicals, Inc.), and tradenames “Terramac TP-4000” and “Terramac TE-4000” (made by UnitikaLimited). Any polylactic acid (A) prepared by a known standardpolymerization method (such as emulsion polymerization and solutionpolymerization) can be used.

The content of the polylactic acid (A) in the polylactic acid film orsheet is usually not less than 60% by weight, preferably not less than70% by weight, more preferably not less than 80% by weight, particularlypreferably not less than 85% by weight from the viewpoint of increase inthe degree of biomass. The upper limit of the content of the polylacticacid (A) is, for example, 97% by weight, preferably 95% by weight, morepreferably 93% by weight. Herein, the degree of biomass refers to theproportion of the dry weight of biomass used to the dry weight of thefilm or sheet. Biomass refers to regenerative organic resources derivedfrom living organisms excluding fossil resources.

In the present invention, the polylactic acid film or sheet used to forma substrate may comprise an acidic functional group-modified olefinpolymer (B). The acidic functional group-modified olefin polymer (B)compounded with the polylactic acid (A) can give rolling lubrication.This property enables the polylactic acid film or sheet to readilyremove from the surfaces of metal rolls when the polylactic acid film orsheet is melt with a calendering film forming machine or the like andpassed through between the metal rolls, leading to smooth filmformation. These acidic functional group-modified olefin polymers (B)may be used singly or in combinations of two or more.

Examples of the acidic functional group of the acidic functionalgroup-modified olefin polymer (B) include a carboxyl group or derivativegroups thereof. Examples of the derivative groups of the carboxyl groupinclude groups chemically derived from a carboxyl group such as acidanhydride groups, ester groups, amide groups, imide groups, and cyanogroups. Among these, an anhydride group is preferable, and a carboxylicanhydride group is more preferable.

The acidic functional group-modified olefin polymer (B) is prepared bygrafting an unsaturated compound containing the “acidic functionalgroup” (hereinafter abbreviated to “acidic functional group-containingunsaturated compound” in some cases) to an unmodified polyolefinpolymer.

Examples of the unmodified polyolefin polymer include polyolefins, suchas high density polyethylene, middle density polyethylene, low densitypolyethylene, polypropylene, polybutene, poly-4-methylpentene-1,copolymers of ethylene and α-olefin, and copolymers of propylene andα-olefin, or oligomers thereof; polyolefin elastomers, such asethylene-propylene rubbers, ethylene-propylene-diene copolymer rubbers,butyl rubbers, butadiene rubbers, low crystalline ethylene-propylenecopolymers, propylene-butene copolymers, ethylene-vinyl estercopolymers, ethylene-methyl (meth)acrylate copolymers, ethylene-ethyl(meth)acrylate copolymers, ethylene-maleic anhydride copolymers, andblends of polypropylene and ethylene-propylene rubbers; and mixturesthereof. Among these, polypropylene, copolymers of propylene andα-olefin, low density polyethylene, and oligomers thereof arepreferable, and polypropylene, copolymers of propylene and α-olefin, andoligomers thereof are particularly preferable. Examples of the“oligomers” include those prepared from the corresponding polymers by amolecular weight degradation method using pyrolysis. The oligomers canalso be prepared by polymerization.

Examples of the acidic functional group-containing unsaturated compoundinclude carboxyl group-containing unsaturated compounds and unsaturatedcompounds containing derivative groups of a carboxyl group. Examples ofthe carboxyl group-containing unsaturated compound include maleic acid,itaconic acid, chloroitaconic acid, chloromaleic acid, citraconic acid,and (meth)acrylic acid. Examples of unsaturated compounds containingderivative groups of a carboxyl group include carboxylic anhydridegroup-containing unsaturated compounds such as maleic anhydride,itaconic anhydride, chloroitaconic anhydride, chloromaleic anhydride,and citraconic anhydride; (meth)acrylates such as methyl (meth)acrylate,glycidyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate; and(meth)acrylamide, maleimide, and (meth)acrylonitrile. Among these, thecarboxyl group-containing unsaturated compounds and the carboxylicanhydride group-containing unsaturated compounds are preferable, acidanhydride group-containing unsaturated compounds are more preferable,and maleic anhydride is particularly preferable.

It is important that the weight average molecular weight of the acidicfunctional group-modified olefin polymer (B) is 10000 to 80000,preferably 15000 to 70000, more preferably 20000 to 60000. A weightaverage molecular weight less than 10000 will cause bleed-out aftermolding of the film or sheet while a weight average molecular weightmore than 80000 will cause the polymer (B) to separate from thepolylactic acid (A) during roll kneading. Herein, bleed-out refers to aphenomenon in which a low molecular weight component comes out of thesurface of the film or sheet after molding of the film or sheet as thetime passes.

The acidic functional group in the acidic functional group-modifiedolefin polymer (B) may modify in any modified proportion or bond to anyposition of the olefin polymer. The acid value of the acidic functionalgroup-modified olefin polymer (B) is usually 10 to 70 mgKOH/g,preferably 20 to 60 mgKOH/g. An acid value less than 10 mgKOH/g cannotattain the effect of improving rolling lubrication while an acid valuemore than 70 mgKOH/g will cause plate out to the roll. Herein, the plateout to the roll refers to a phenomenon in which during melt film formingof a resin composition using a metal roll, components compounded withthe resin composition or oxidized, decomposed, combined, or degradedproducts thereof, etc. adhere to or deposit on the surface of the metalroll. In the present invention, the “acid value” refers to the valuemeasured according to JIS K0070-1992: Neutralization Titration.

The acidic functional group-modified olefin polymer (B) is prepared byreacting the unmodified polyolefin polymer with the acidic functionalgroup-containing unsaturated compound in the presence of an organicperoxide. Any organic peroxide used as a standard initiator in radicalpolymerization can be used. The reaction can be performed by any of asolution method and a melting method. In the solution method, the acidicfunctional group-modified olefin polymer (B) can be prepared bydissolving a mixture of the unmodified polyolefin polymer and the acidicfunctional group-containing unsaturated compound with an organicperoxide in an organic solvent, and heating the mixture. The reactiontemperature is preferably approximately 110 to 170° C.

In the melting method, the acidic functional group-modified olefinpolymer (B) can be prepared by mixing a mixture of the unmodifiedpolyolefin polymer and the acidic functional group-containingunsaturated compound with an organic peroxide, and reacting the mixtureby melt mixing. Melt mixing can be performed with a variety of mixerssuch as extruders, Brabenders, kneaders, and Banbury mixers. Thekneading temperature is usually within the temperature range of themelting point of the unmodified polyolefin polymer to 300° C.

The acidic functional group-modified olefin polymer (B) is preferablymaleic anhydride modified polypropylene. Commercially available productscan be used as the acidic functional group-modified olefin polymer (B),and examples thereof include trade names “Umex 1010” (maleic anhydridegroup-modified polypropylene, acid value: 52 mgKOH/g, weight averagemolecular weight: 32000, modified proportion: 10% by weight), “Umex1001” (maleic anhydride group-modified polypropylene, acid value: 26mgKOH/g, weight average molecular weight: 49000, modified proportion: 5%by weight), “Umex 2000” (maleic anhydride group-containing modifiedpolyethylene, acid value: 30 mgKOH/g, weight average molecular weight:20000, modified proportion: 5% by weight) made by Sanyo ChemicalIndustries, Ltd.

The acidic functional group-modified olefin polymer (B) in thepolylactic acid film or sheet can be used in any content. For example,0.1 to 10 parts by weight of the acidic functional group-modified olefinpolymer (B) having an acid value of 10 to 70 mgKOH/g and a weightaverage molecular weight of 10000 to 80000 may be contained based on 100parts by weight of the polylactic acid (A) (or a composition comprisingthe polylactic acid (A) and the reforming agent (E) when the reformingagent (E) is contained). The content thereof is preferably 0.1 to 5parts by weight, particularly preferably 0.3 to 3 parts by weight fromthe viewpoint of maintenance of the effect of rolling lubricationwithout plate out to the roll and maintenance of the degree of biomass.Less than 0.1 parts by weight of the acidic functional group-modifiedolefin polymer (B) is difficult to attain the effect of improvingrolling lubrication while more than 10 parts by weight of the acidicfunctional group-modified olefin polymer (B) cannot attain the effectaccording to the amount of addition, and reduces the degree of biomass.

In the present invention, the polylactic acid film or sheet used to formthe substrate may contain a fluorine-containing polymer (C) in additionto the components above. The fluorine-containing polymer (C) is used asa melt tension adjuster or a crystallization promoter, for example.Examples of the fluorine-containing polymer (C) includetetrafluoroethylene polymers, polychlorotrifluoroethylene,polyvinylidene fluoride, and polyvinyl fluoride. Thesefluorine-containing polymers (C) may be used singly or in combinationsof two or more. Particularly, tetrafluoroethylene polymer (C′) can besuitably used as the fluorine-containing polymer (C).

The tetrafluoroethylene polymer (C′) may be a homopolymer oftetrafluoroethylene or a copolymer of tetrafluoroethylene and anadditional monomer. Examples of the tetrafluoroethylene polymer (C′)include polytetrafluoroethylene, perfluoroalkoxyalkane (copolymers oftetrafluoroethylene and perfluoroalkylvinylether), perfluoroethylenepropene copolymers (copolymers of tetrafluoroethylene andhexafluoropropylene), ethylene-tetrafluoroethylene copolymers, andtetrafluoroethylene-perfluorodioxol copolymers. Among these,polytetrafluoroethylene is preferable. These tetrafluoroethylenepolymers (C′) may be used singly or in combinations of two or more.

If the fluorine-containing polymer (C) is compounded with the polylacticacid (A)-containing resin composition, melt tension is improved and meltviscosity is increased. For example, in film formation with a calenderroll, these properties can prevent elongation and peel-off failure,which might be caused when the resin composition formed into a film isremoved from the roll. Particularly, fluorine-containing polymers suchas the tetrafluoroethylene polymer (C′) serve as a nucleator for thepolylactic acid (A). Such polymers can further promote crystallizationof the polylactic acid (A) by setting the temperature of the resincomposition immediately after film formation at a temperature close tothe crystallization temperature thereof. As above, thefluorine-containing polymer (C) [particularly tetrafluoroethylenepolymer (C′)] compounded can promote crystallization of the polylacticacid (A).

It seems that the action as a nucleator of the tetrafluoroethylenepolymer (C′) on the polylactic acid (A) depends on the crystal structureof the tetrafluoroethylene polymer (C′). According to the determinationby wide angle X ray diffraction, the crystal lattice of polylactic acidhad a plane interval of 4.8 angstroms while tetrafluoroethylene polymer(C′) had a plane interval of 4.9 angstroms. From this, it is consideredthat the tetrafluoroethylene polymer (C′) has an epitaxy effect, and canserve as a nucleator for the polylactic acid (A). Herein, the epitaxyeffect refers to a manner of growth in which the polylactic acid (A)crystal grows on the surface of the tetrafluoroethylene polymer (C′) toalign the polylactic acid (A) along the crystal planes on the crystalsurface of the tetrafluoroethylene polymer (C′).

The plane interval of the tetrafluoroethylene polymer (C′) and that of acopolymer of tetrafluoroethylene and an additional monomer both aregoverned by the form of crystal of a tetrafluoroethylene portion, andthe plane intervals thereof are the same. Accordingly, the copolymer cancontain the additional monomer component in any content to the extentthat the form of crystal of polytetrafluoroethylene can be kept andphysical properties do not change much. Desirably, the proportion of theadditional monomer component in the tetrafluoroethylene polymer (C′) isusually not more than 5% by weight.

The tetrafluoroethylene polymer (C′) can be prepared by anypolymerization method, and those prepared by emulsion polymerization areparticularly preferable. The tetrafluoroethylene polymer prepared byemulsion polymerization readily turns into fibers to have a networkstructure in the polylactic acid (A). This structure probablyeffectively serves to improve the melt tension of the resin compositioncontaining the polylactic acid (A).

To uniformly disperse the tetrafluoroethylene polymer (C′) in thepolylactic acid (A), particles of the tetrafluoroethylene polymer (C′)modified with a polymer having good affinity with the polylactic acid(A), such as a (meth)acrylate polymer, may be used. Examples of such atetrafluoroethylene polymer (C′) include acrylic-modifiedpolytetrafluoroethylene.

The fluorine-containing polymer (C) [such as the tetrafluoroethylenepolymer (C′)] can have any weight average molecular weight. The weightaverage molecular weight is usually 1000000 to 10000000, preferably2000000 to 8000000.

Commercially available products may be used as the fluorine-containingpolymer (C) [such as the tetrafluoroethylene polymer (C′)]. Examples ofcommercially available products of polytetrafluoroethylene include tradenames “Fluon CD-014,” “Fluon CD-1,” and “Fluon CD-145” made by ASAHIGLASS CO., LTD. Examples of commercially available products ofacrylic-modified polytetrafluoroethylene include METABLEN A series suchas trade names “METABLEN A-3000” and “METABLEN A-3800” made byMITSUBISHI RAYON CO., LTD.

The polylactic acid film or sheet can contain the fluorine-containingpolymer (C) [particularly, the tetrafluoroethylene polymer (C′)] in anycontent. For example, the polylactic acid film or sheet can contain 0.5to 15 parts by weight of the fluorine-containing polymer (C) based on100 parts by weight of the polylactic acid (A) (or a compositioncomprising the polylactic acid (A) and the reforming agent (E) when thereforming agent (E) is contained). The content of thefluorine-containing polymer (C) is preferably 0.7 to 10 parts by weight,more preferably 1 to 5 parts by weight from the viewpoint of the effectof improving melt tension, maintenance of the degree of biomass, andachievement of a good surface state. If the content of thefluorine-containing polymer (C) [particularly, content of thetetrafluoroethylene polymer (C′)] is less than 0.5 parts by weight, theeffect of improving melt tension is difficult to attain. If the contentis more than 15 parts by weight, the effect according to the amount ofaddition cannot be attained, and the degree of biomass reduces.

The polylactic acid film or sheet can be produced by any specificmethod, and examples thereof include (1) forming the resin compositioncontaining the polylactic acid (A) into a film by a melt film formingmethod such as calendering, (2) forming a resin composition comprisingthe polylactic acid (A) and a crystallization promoter into a film, and(3) a combination thereof. The melt film forming method will bedescribed later.

The crystallization promoter other than the fluorine-containing polymerusable as the crystallization promoter [such as the tetrafluoroethylenepolymer (C′)] among the fluorine-containing polymers (C) can be used asthe crystallization promoter. Such a crystallization promoter [referredto as crystallization promoter (D) in some cases] can be used withoutlimitation as long as it is found to have the effect of promotingcrystallization. Desirably, a substance having a crystal structure witha plane interval close to the plane interval of the crystal lattice ofthe polylactic acid (A) is selected. This is because as the planeinterval of the crystal lattice of the substance is closer to the planeinterval of the crystal lattice of the polylactic acid (A), thesubstance has a high effect as the nucleator for the polylactic acid(A). Examples of such a crystallization promoter (D) include organicsubstances such as polyphosphoric acid melamine, melamine cyanurate,zinc phenyl phosphonate, calcium phenyl phosphonate, and magnesiumphenyl phosphonate; and inorganic substances such as talc and clay.Among these, zinc phenyl phosphonate is preferable because thissubstance has a plane interval closest to the plane interval of thepolylactic acid (A) to attain a good effect of promotingcrystallization. These crystallization promoters (D) may be used singlyor in combinations of two or more.

Commercially available products can be used as the crystallizationpromoter (D). Examples of commercially available products of zinc phenylphosphonate include trade name “ECOPROMOTE” made by Nissan ChemicalIndustries, Ltd.

The polylactic acid film or sheet can contain the crystallizationpromoter (D) in any content. For example, the polylactic acid film orsheet contains 0.1 to 15 parts by weight of the crystallization promoter(D) based on 100 parts by weight of the polylactic acid (A) (or acomposition comprising the polylactic acid (A) and the reforming agent(E) when the reforming agent (E) is contained). The content ispreferably 0.3 to 10 parts by weight from the viewpoint of a high effectof promoting crystallization and maintenance of the degree of biomass.At a content of the crystallization promoter (D) less than 0.1 parts byweight, the effect of promoting crystallization is difficult to attain.At a content more than 15 parts by weight, the effect according to theamount of addition cannot be attained, and the degree of biomassreduces. When 0.1 to 15 parts by weight of the tetrafluoroethylenepolymer (C′) as the fluorine-containing polymer (C) is used based on 100parts by weight of the polylactic acid (A) (or a composition comprisingthe polylactic acid (A) and the reforming agent (E) when the reformingagent (E) is contained), the content of the crystallization promoter (D)is preferably 0.1 to 5 parts by weight, more preferably 0.3 to 3 partsby weight based on 100 parts by weight of the polylactic acid (A) (or acomposition comprising the polylactic acid (A) and the reforming agent(E) when the reforming agent (E) is contained) from the viewpoint of ahigh effect of promoting crystallization and maintenance of the degreeof biomass. In this case, at a content of the crystallization promoter(D) less than 0.1 parts by weight, the effect of promotingcrystallization is difficult to attain. At a content more than 5 partsby weight, the effect according to the amount of addition cannot beattained, and the degree of biomass reduces.

In the present invention, the polylactic acid film or sheet has a tearstrength of not less than 100 N/mm, preferably not less than 150 N/mmwhen the film or sheet is torn at least in the flow direction (MD). Ifthe polylactic acid film or sheet having such a tear strength is used asthe substrate for the protection film, the substrate does not break ortear during producing or processing the protection film including a stepof applying tension. The substrate does not break or tear during windingof the protection film into a roll or a process such punching.Furthermore, the protection film does not break or tear when theprotection film is re-attached in use or is finally peeled.

In the present invention, the tear strength can be determined accordingto JIS K7128-3: Plastics—Film and Sheeting—Determination of TearResistance, Part 3: Right angled tear method. As described above, thepolylactic acid film or sheet having a tear strength of not less than100 N/mm when the film or sheet is torn at least in the flow direction(MD) does not break or tear not only during production of the film orsheet but also during winding thereof into a roll or processing thereof.This property enables various processes, widening its application rangesignificantly.

In the present invention, the polylactic acid film or sheet has a rateof dimensional change due to heating of not more than ±3%, preferablynot more than ±2%, not more than ±1% in the flow direction (MD) and thetransverse direction (TD). When the polylactic acid film or sheet havingsuch a rate of dimensional change due to heating is used as thesubstrate for the protection film, the film or sheet does not melt ordeform under high temperature conditions more than 100° C., for example,and can be sufficiently used in applications requiring heat resistance.

In the present invention, when the film or sheet is stored under anatmosphere at 100° C. for 1 minute, the rate of dimensional change dueto heating is determined by Expression (1):

rate of dimensional change due to heating (%)=(L2 −L1)/L1×100  (1)

where L1 represents a gauge length before a test, and L2 represents agauge length after the test.

In the present invention, the polylactic acid film or sheet has a rateof dimensional change due to loaded heating of not more than ±3%,preferably not more than ±2%, not more than ±1% in the flow direction(MD) and the transverse direction (TD). When the polylactic acid film orsheet having such a rate of dimensional change due to loaded heating isused as the substrate for the protection film, the film or sheet doesnot melt or deform under high temperature conditions of more than 100°C., for example, and can be sufficiently used in applications requiringheat resistance.

In the present invention, when the film or sheet is stored under anatmosphere at 100° C. for 1 minute while a load of 300 g/mm² is appliedin the flow direction (MD), the rate of dimensional change due to loadedheating is determined by Expression (2):

rate of dimensional change due to loaded heating (%)=(L4−L3)/L3×100  (2)

where L3 represents a gauge length before a test, and L4 represents agauge length after the test.

In the present invention, examples of a specific method for furtherimproving physical properties of the polylactic acid film or sheetinclude a method of compounding the reforming agent (E) with thepolylactic acid (A) to prepare a resin composition and forming the resincomposition into a film.

Examples of the reforming agent (E) include polyglycerol fatty acidesters or polyglycerol condensed hydroxy fatty acid esters (a),core-shell-structured polymers (b) composed of a particulate rubber anda graft layer formed on the outside of the rubber, and soft aliphaticpolyesters (c). These may be each used singly or in combinations of twoor more.

In the present invention, the polylactic acid film or sheet contains thepolyglycerol fatty acid ester and/or polyglycerol condensed hydroxyfatty acid ester (a) as the reforming agent (E) such that the weightratio of the polylactic acid (A) to the polyglycerol fatty acid esterand/or polyglycerol condensed hydroxy fatty acid ester (a) is preferably99:1 to 80:20 ((A):total amount of (a)), more preferably 95:5 to 90:10((A):total amount of (a)). These polyglycerol fatty acid esters andpolyglycerol condensed hydroxy fatty acid esters may be each used singlyor in combinations of two or more.

An excessively small amount of the polyglycerol fatty acid ester and/orpolyglycerol condensed hydroxy fatty acid ester (a) leads to aninsufficient effect of reforming physical properties. An excessivelylarge amount of the polyglycerol fatty acid ester and/or polyglycerolcondensed hydroxy fatty acid ester (a) readily reduces the degree ofcrystallization and the rate of crystallization, and may cause thepolyglycerol fatty acid ester and/or polyglycerol condensed hydroxyfatty acid ester (a) to bleed out. When the polylactic acid film orsheet containing the polyglycerol fatty acid ester or polyglycerolcondensed hydroxy fatty acid ester (a) in the above range is used as thesubstrate for the protection film, tear resistance can be improvedwithout reducing heat resistance.

In the polyglycerol fatty acid ester or polyglycerol condensed hydroxyfatty acid ester (a), polyglycerol fatty acid ester is prepared by areaction of polyglycerol with fatty acid. Examples of the constituent ofthe polyglycerol fatty acid ester, i.e., polyglycerol, includediglycerol, triglycerol, tetraglycerol, pentaglycerol, hexaglycerol,heptaglycerol, octaglycerol, nonaglycerol, decaglycerol, anddodecaglycerol. These are used singly or as a mixture. The averagedegree of polymerization of polyglycerol is preferably 2 to 10.

For the other constituent of the polyglycerol fatty acid ester, i.e.,fatty acid, fatty acids having not less than 12 carbon atoms are used,for example. Specific examples of the fatty acids include lauric acid,myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid,linolenic acid, eicosadienoic acid, arachidonic acid, behenic acid,erucic acid, ricinoleic acid, 12-hydroxystearic acid, and hydrogenatedcastor oil fatty acids. These are used singly or as a mixture.

Polyglycerol condensed hydroxy fatty acid ester is prepared by areaction of polyglycerol and condensed hydroxy fatty acid. Examples ofthe constituent of the polyglycerol condensed hydroxy fatty acid ester,i.e., polyglycerol include those exemplified as the constituent of thepolyglycerol fatty acid ester.

The condensed hydroxy fatty acid as the other constituent of thepolyglycerol condensed hydroxy fatty acid ester is a condensed productof a hydroxy fatty acid. Any hydroxy fatty acid having one or morehydroxyl groups in the molecule can be used, and examples thereofinclude ricinoleic acid, 12-hydroxystearic acid, and hydrogenated castoroil fatty acids. The degree of condensation of condensed hydroxy acidis, for example, not less than 3, preferably 3 to 8. The condensedhydroxy fatty acids are used singly or as a mixture.

Commercially available products can be used as the polyglycerol fattyacid ester and the polyglycerol condensed hydroxy fatty acid ester.Examples of commercially available products of the polyglycerol fattyacid ester include Chirabasol series such as trade names “ChirabasolVR-10” and “Chirabasol VR-2” made by Taiyo Kagaku Co., Ltd.

In the present invention, the polylactic acid film or sheet contains thecore-shell-structured polymer (b) composed of a particulate rubber and agraft layer formed on the outside of the rubber as the reforming agent(E) such that the weight ratio of the polylactic acid (A) to thecore-shell-structured polymer (b) composed of a particulate rubber and agraft layer formed on the outside of the rubber is preferably 99:1 to80:20 ((A):(b)), more preferably 97:3 to 90:10 ((A):(b)). Thecore-shell-structured polymers (b) composed of a particulate rubber anda graft layer formed on the outside of the rubber may be used singly orin combinations of two or more.

An excessively small amount of the core-shell-structured polymer (b)composed of a particulate rubber and a graft layer formed on the outsideof the rubber leads to an insufficient effect of reforming physicalproperties. An excessively large amount of the core-shell-structuredpolymer (b) composed of a particulate rubber and a graft layer formed onthe outside of the rubber readily reduces the degree of crystallizationand the rate of crystallization, and may cause the core-shell-structuredpolymer (b) composed of a particulate rubber and a graft layer formed onthe outside of the rubber to bleed out. When the polylactic acid film orsheet containing the core-shell-structured polymer (b) composed of aparticulate rubber and a graft layer formed on the outside of the rubberin the above range is used as the substrate for the protection film,tear resistance can be improved without reducing heat resistance.

Examples of the particulate rubber that forms the core in thecore-shell-structured polymer (b) composed of a particulate rubber and agraft layer formed on the outside of the rubber include acrylic rubbers,butadiene rubbers, and silicone-acrylic composite rubbers.

Examples of a polymer that forms the shell include styrene resins suchas polystyrene, and acrylic resins such as polymethyl methacrylate.

The average particle size of the core-shell-structured polymer (a set ofprimary particles) is, for example, 50 to 500 μm, preferably 100 to 250μm. When this polymer is compounded with the polylactic acid (A) and ismelt kneaded, its primary particles are dispersed. The primary particleshave an average particle size of 0.1 to 0.6 μm, for example.

Commercially available products can be used as the core-shell-structuredpolymer. Examples of commercially available products of thecore-shell-structured polymer include PARALOID series (particularly,PARALOID EXL series) such as trade name “PARALOID EXL2315” made by Rohmand Haas Japan K.K., and METABLEN S type such as trade name “METABLENS-2001,” METABLEN W type such as trade name “METABLEN W-450A,” METABLENC type such as trade name “METABLEN C-223A,” and METABLEN E type such astrade name “METABLEN E-901” made by MITSUBISHI RAYON CO., LTD.

In the present invention, the polylactic acid film or sheet contains thesoft aliphatic polyester (c) as the reforming agent (E) such that theweight ratio of the polylactic acid (A) to the soft aliphatic polyester(c) is preferably 95:5 to 60:40 ((A):(c)), more preferably 90:10 to80:20 ((A):(c)). The soft aliphatic polyesters (c) may be used singly orin combinations of two or more.

An excessively small amount of the soft aliphatic polyester (c) leads toan insufficient effect of reforming physical properties. An excessivelylarge amount of the soft aliphatic polyester (c) readily reduces thedegree of crystallization and the rate of crystallization, and may causethe soft aliphatic polyester (c) to bleed out. When the polylactic acidfilm or sheet containing the soft aliphatic polyester (c) in the aboverange is used as the substrate for the protection film, tear resistancecan be improved without reducing heat resistance.

The soft aliphatic polyester (c) includes aliphatic polyesters andaliphatic and aromatic copolymerization polyesters. The soft aliphaticpolyester (c) (aliphatic polyesters and aliphatic and aromaticcopolymerization polyesters) is prepared from a polyhydric alcohol suchas diol and a polyvalent carboxylic acid such as dicarboxylic acid, andexamples thereof include polyesters comprising at least an aliphaticdiol as diol and at least an aliphatic dicarboxylic acid as dicarboxylicacid; and polymers of aliphatic hydroxycarboxylic acids having not lessthan 4 carbon atoms. Examples of the aliphatic diol include aliphaticdiols having 2 to 12 carbon atoms (including alicyclic diols) such asethylene glycol, 1,2-propanediol, 1,3-propanediol,2,2-dimethyl-1,3-propanediol, 1,2-butanediol, 1,4-butanediol, neopentylglycol, 1,5-pentanediol, 1,6-hexanediol, cyclohexanediol,1,3-cyclohexanedimethanol, and 1,4-cyclohexanedimethanol. Examples ofthe aliphatic dicarboxylic acid include saturated aliphatic dicarboxylicacid having 2 to 12 carbon atoms (including alicyclic dicarboxylicacids) such as succinic acid, malonic acid, glutaric acid, adipic acid,pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioicacid, 1,3-cyclohexanedicarboxylic acid, and 1,4-cyclohexanedicarboxylicacid. In the polyesters comprising at least an aliphatic diol as thediol component and at least an aliphatic dicarboxylic acid as thedicarboxylic acid component, the proportion of the aliphatic diol to theentire diol component is, for example, not less than 80% by weight,preferably not less than 90% by weight, more preferably not less than95% by weight. Besides the aliphatic diol, aromatic diol or the like maybe contained. In the polyesters comprising at least an aliphatic diol asthe diol component and at least an aliphatic dicarboxylic acid as thedicarboxylic acid component, the proportion of the aliphaticdicarboxylic acid to the entire dicarboxylic acid component is forexample, not less than 20% by weight, preferably not less than 30% byweight, more preferably not less than 50% by weight. Besides thealiphatic dicarboxylic acid, aromatic dicarboxylic acid (such asterephthalic acid) may be contained. Examples of the aliphatichydroxycarboxylic acid having not less than 4 carbon atoms includehydroxycarboxylic acids having 4 to 12 carbon atoms such ashydroxybutyric acid, hydroxyvaleric acid, hydroxypentanoic acid,hydroxyhexanoic acid, hydroxydecanoic acid, and hydroxydodecanoic acid.The soft aliphatic polyester (c) (aliphatic polyesters and aliphatic andaromatic copolymerization polyesters) has a weight average molecularweight of, for example, 50000 to 400000, preferably 80000 to 250000.

Typical examples of the soft aliphatic polyester (c) includepolybutylene succinate, polybutylene succinate adipate, polyethylenesuccinate, polyethylene succinate adipate, polybutylene adipateterephthalate, polybutylene sebacate terephthalate, andpolyhydroxylalkanoate.

Commercially available products can be used as the soft aliphaticpolyester (c). Examples of polybutylene succinate include trade name “GSPla AZ91T” made by Mitsubishi Chemical Corporation, examples ofpolybutylene succinate adipate include trade name “GS Pla AD92W” made byMitsubishi Chemical Corporation, and examples of polybutylene adipateterephthalate include trade name “Ecoflex” made by BASF Japan Ltd.

In the present invention, the polylactic acid film or sheet mayoptionally contain a variety of additives in the range not to impair theeffects of the present invention. Examples of such additives includeantioxidants, ultraviolet absorbing agents, plasticizers, stabilizers,mold release agents, antistatic agents, colorants (such as whitepigments), drip preventing agents, flame retardants, hydrolysispreventing agents, foaming agents, and fillers.

In the present invention, the polylactic acid film or sheet, which hashigh degree of crystallization, also has high solvent resistance. Forexample, the polylactic acid film or sheet has a degree of swelling offor example, not more than 2.5, preferably not more than 2.0 to anysolvent of ethyl acetate and toluene. The degree of swelling can bedetermined as follows: A film or sheet sample (50 mm×50 mm×thickness of0.05 mm) is immersed in a solvent for 15 minutes, and is taken out fromthe solvent; then, the solvent on the surface of the sample is removedwith a waste cloth, and the weight of the sample after immersion isdivided by that before immersion.

In the present invention, the polylactic acid film or sheet can alsomaintain high mechanical properties such as rigidity and highelasticity. For example, the polylactic acid film or sheet in thepresent invention has an initial elastic modulus of usually not lessthan 1000 MPa, preferably not less than 1500 MPa in the flow direction(MD). The upper limit of the initial elastic modulus is typicallyapproximately 3500 MPa (for example, approximately 3000 MPa) in the flowdirection (MD). The polylactic acid film or sheet in the presentinvention has a breaking strength of usually not less than 30 MPa,preferably not less than 35 MPa in the flow direction (MD). The upperlimit of the breaking strength is typically approximately 150 MPa (forexample, approximately 120 MPa).

The polylactic acid film or sheet in the present invention has anelongation of usually not less than 2.5%, preferably not less than 3.5%in the flow direction (MD). The upper limit of the elongation istypically approximately 15% (for example, approximately 12%) in the flowdirection (MD). When the soft aliphatic polyester (c) is used as thereforming agent (E), the polylactic acid film or sheet has an elongationof usually not less than 5%, preferably not less than 10%, morepreferably not less than 20% in the flow direction (MD). The upper limitof the elongation is typically 150%, preferably 120%, more preferably100% in the flow direction (MD).

The initial elastic modulus, the breaking strength, and the elongationwere determined with a tensile tester according to JIS K 7161:Plastics—Determination of tensile properties.

apparatus: tensile tester (Autograph AG-20kNG, manufactured by SHIMADZUCorporation) sample size: thickness of 0.05 mm×width of 10 mm×length of100 mm (a sample was cut out such that the direction of the sampleparallel to the length direction of the film or sheet corresponded tothe flow direction (MD) in film formation)

Measurement Condition:

distance between chucks: 50 mm

tensile rate: 300 ram/min

In the present invention, the polylactic acid film or sheet can have anythickness, which is usually 10 to 500 μm, preferably 20 to 400 μm, morepreferably 30 to 300 μm.

[Method of Producing Protection Film]

The method of producing a polylactic acid film or sheet in the presentinvention is

a method of producing a protection film comprising a substrate composedof a polylactic acid film or sheet prepared by forming a resincomposition comprising polylactic acid (A) into a film by a melt filmforming method, the method comprising:

a melt film forming step of melt forming the resin composition,

a cooling solidifying step of cooling and solidifying the resincomposition after the melt film forming step to prepare a film or sheet,and

a crystallization promoting step of heating the film or sheet after thecooling solidifying step to promote crystallization of the film orsheet,

wherein a resin temperature in the melt film forming step is within therange of (Tm) −15° C. to (Tm) +15° C. where Tm represents a meltingtemperature of the resin composition during raising of temperature, and

in at least part of the crystallization promoting step, crystallizationof the film or sheet is promoted within the temperature range of (Tc)+10° C. to (Tc) +50° C. where Tc represents a crystallizationtemperature of the resin composition during the raising of temperature.

For example, the polylactic acid film or sheet can be produced with acontinuous melt kneader with a twin screw extruder or the like, or abatch type melt kneader such as a pressure kneader, a Banbury mixer, aroll kneader by uniformly dispersing the components to prepare a resincomposition containing the polylactic acid (A), forming the resincomposition into a film by extrusion such as a T die method and aninflation method, calendering, or polishing, and cooling and solidifyingthe film. The melt film forming method is a method in which preferably amelt resin composition is passed through between two metal rolls to beformed into a film of a desired thickness. The method is more preferablycalendering or polishing, particularly preferably calendering.

The resin temperature in the melt film forming step is within the rangeof (Tm) −15° C. to (Tm) +15° C., preferably (Tm) −15° C. to (Tm) +5° C.,more preferably (Tm) −10° C. to (Tm), particularly preferably (Tm) −5°C. to (Tm) where Tm represents a melting temperature of the resincomposition during raising of temperature.

In particular, when the resin composition does not contain the reformingagent (E), the resin temperature is within the range of preferably (Tm)−15° C. to (Tm) +5° C., more preferably (Tm) −10° C. to (Tm) where Tmrepresents a melting temperature of the resin composition during raisingof temperature.

In particular, when the resin composition further contains the reformingagent (E), the resin temperature is within the range of preferably (Tm)−10° C. to (Tm) +5° C., more preferably (Tm) −5° C. to (Tm) where Tmrepresents a melting temperature of the resin composition during raisingof temperature.

The resin temperature set within such a range attains an effect ofsuppressing oriented crystallization during film formation.

In particular, from the viewpoint of consistent control to be apredetermined temperature, it is desired that in the melt film formingstep, the resin composition be contacted with a metal roll having apredetermined surface temperature. Accordingly, also in the step, theresin composition containing the polylactic acid (A) is desirably formedof a composition readily peelable from the metal roll. From theviewpoint, addition of the acidic functional group-modified olefinpolymer (B) is preferable.

The method of producing a protection film in the present inventionpreferably comprises a residual stress relaxing step after the melt filmforming step and before the cooling solidifying step, the step ofkeeping the resin composition within a predetermined temperature rangeto relax the residual stress of the resin composition. The predeterminedtemperature (residual stress relaxing temperature) can be anytemperature, for example, within the temperature range of (Tm) −70° C.to (Tm) −20° C., preferably (Tm) −60° C. to (Tm) −20° C., morepreferably (Tm) −60° C. to (Tm) −23° C., still more preferably (Tm) −50°C. to (Tm) −25° C., particularly preferably (Tm) −50° C. to (Tm) −30° C.

In particular, when the resin composition does not contain the reformingagent (E), the residual stress relaxing temperature is within thetemperature range of preferably (Tm) −60° C. to (Tm) −23° C., morepreferably (Tm) −50° C. to (Tm) −30° C.

In particular, when the resin composition further contains the reformingagent (E), the residual stress relaxing temperature is within thetemperature range of preferably (Tm) −60° C. to (Tm) −20° C., morepreferably (Tm) −60° C. to (Tm) −23° C., still more preferably (Tm) −50°C. to (Tm) −25° C., particularly preferably (Tm) −50° C. to (Tm) −30° C.The preferred temperature range may depend on types of the reformingagent (E) or the like.

The residual stress relaxing temperature set within such a range furtherenhances the effect of relaxing the residual stress and further reducesthe risk of extremely thermally shrinking the prepared film or sheetduring usage. This setting of the residual stress relaxing temperatureenables the resultant crystallized film or sheet to keep the shape up toa temperature close to the melting point of polylactic acid. Such a filmor sheet can be sufficiently used in applications requiring heatresistance, in which the film or sheet have not been able to be used.The residual stress relaxing step can use any specific method of keepingthe resin composition at a predetermined temperature. Examples thereofinclude a method of contacting a film sample with a take-off roll keptat a predetermined temperature.

In at least part of the crystallization promoting step, crystallizationof the film or sheet is promoted within the temperature range of (Tc)+10° C. to (Tc) +50° C. where Tc represents a crystallizationtemperature of the resin composition during the raising of temperature.Crystallization of the film or sheet is promoted within the temperaturerange of preferably (Tc) +20° C. to (Tc) +45° C., more preferably (Tc)+20° C. to (Tc) +40° C. where Tc represents a crystallizationtemperature of the resin composition during the raising of temperature.The crystallization temperature set within such a temperature rangefurther improves the effect of promoting crystallization to improve aproduction rate.

In particular, from the viewpoint of consistent control to be apredetermined temperature, it is desired that in the crystallizationpromoting step, the film or sheet be contacted with a metal roll havinga predetermined surface temperature. Accordingly, also in the step, thefilm or sheet is desirably formed of a composition readily peelable fromthe metal roll. From the viewpoint, addition of the acidic functionalgroup-modified olefin polymer (B) is preferable.

The time for the crystallization promoting step is preferably as long aspossible. The time depends on the degree of crystallization of the resincomposition as a conclusion and cannot be specified in general. The timeis usually 10 to 120 seconds, preferably 20 to 90 seconds, morepreferably 30 to 60 seconds.

In the crystallization promoting step, an optimal temperature conditionfor the crystallization promoting step can always be obtained, even ifthe crystallization temperature (Tc) changes due to addition of anadditional nucleator or the like during lowering of temperature of theresin composition, by determining the temperature at the highestexothermic peak accompanied by crystallization during lowering oftemperature in advance in the measurement with a differential scanningcalorimeter (DSC). At this time, it is barely necessary to considerchanges in the shape of the film or sheet prepared which are caused byheating at the temperature. Preferably, the temperature attains a filmor sheet having a thermal deformation rate of not more than 40%.

Before and/or after the crystallization promoting step, monoaxial ortwin-axial drawing (preferably twin-axial drawing) may be performed. Thedrawing may further increase crystallization. The drawing temperatureis, for example, 60 to 100° C.

In the method of producing a polylactic acid film or sheet comprisingthe crystallization promoting step, the steps from the melt film formingstep to the cooling solidifying step are continuously performed. Thiscontinuous mode is preferable for a reduction in the process time, andthus productivity. More preferably, the crystallization step is providedcontinuously subsequent to the cooling solidifying step (for example,the film or sheet is passed through a heat roll). Examples of such amethod include methods using a calendering film forming machine, apolishing film forming machine, or the like.

[Calendering Film Formation]

A schematic view of an example of a calendering film forming machineused in the production method will be shown in FIG. 1. Hereinafter, FIG.1 will be described in detail.

While a first roll 1, a second roll 2, a third roll 3, and a fourth roll4 are being controlled, a melt resin composition is rolled between thesefour calender rolls to be gradually thinned, and is controlled to have adesired thickness finally when the resin composition is passed throughbetween the third roll 3 and the fourth roll 4. In the calendering filmformation, film formation of the resin composition from the first roll 1to the fourth roll 4 corresponds to the “melt film forming step.” Atake-off roll 5 represents a group of rolls contacted by a resincomposition 8 formed into a film by melt film forming first. Thetake-off roll 5 includes one or two or more (three in FIG. 1) rolls,which peel off the melt resin composition 8 from the fourth roll 4. Whenthe take-off roll 5 includes a plurality of rolls as above and thetemperatures of the respective rolls can be controlled, the temperaturesof the respective rolls are preferably the same. The temperatures may bedifferent if the temperatures fall within a desired temperature range.

The take-off roll 5 contacts with the film sample to relax the residualstress (residual stress relaxing step). At this time, the (three inFIG. 1) take-off rolls often have approximately the same surfacetemperature, which is the stress relaxing temperature (° C.). The threetake-off rolls may have different temperatures. In this case,preferably, the temperatures of these take-off rolls are within thetemperature range above.

Two cooling rolls 6 and 7 cool the resin composition 8 when the resincomposition 8 is passed through between these rolls, thereby to solidifythe resin composition 8 and mold the surface into a desired shape(cooling solidifying step). For this reason, typically, one roll (forexample, cooling roll 6) is a metal roll having a designed surface toproduce the shape of the surface of the resin composition 8, and theother roll (for example, cooling roll 7) is a rubber roll. Arrows in thedrawing represent rotational directions of the respective rolls. A bank9 (resin pool) is shown.

Subsequently, the cooled and solidified film is heated with a heat rollnot shown in FIG. 1 controlled to be any temperature to promotecrystallization (crystallization promoting step).

[Polishing Film Formation]

A schematic view of an example of a polishing film forming machine usedin the production method will be shown in FIG. 2. Hereinafter, FIG. 2will be described in detail.

A tip 10 of an extruder (not shown) is disposed between a second roll 2and a third roll 3 heated, and a melt resin composition 8 iscontinuously extruded between the second roll 2 and the third roll 3 ata preset extrusion rate. The extruded resin composition 8 is rolledbetween the second roll 2 and the third roll 3 to be thinned, and iscontrolled to have a desired thickness finally when the resincomposition 8 is passed through between the third roll 3 and the fourthroll 4. In polishing film formation, the film formation of the resincomposition 8 from the second roll 2 to the fourth roll 4 corresponds tothe “melt film forming step.” Subsequently, the resin composition 8 ispassed through one or two or more (three in FIG. 2) take-off rolls 5(residual stress relaxing step), and finally passed through the coolingroll (cooling rolls 6 and 7 in FIG. 2) (cooling solidifying step) toprepare a solidified film or sheet.

Subsequently, the cooled and solidified and formed film is heated with aheat roll not shown in FIG. 2 controlled to be any temperature topromote crystallization (crystallization promoting step).

In the present invention, to enhance the adhesion to an adjacent layer,the surface of the substrate may be optionally subjected to a standardsurface treatment, for example, an oxidation treatment by a chemical orphysical method, such as chromic acid treatment, exposure to ozone,exposure to flame, exposure to high voltage electric shock, andionization radiation treatment.

[Removable Pressure-Sensitive Adhesive Layer]

The protection film according to the present invention includes aremovable pressure-sensitive adhesive layer on at least one surface ofthe substrate.

The removable pressure-sensitive adhesive layer can be composed of anyknown pressure-sensitive adhesive, and examples thereof include rubberpressure-sensitive adhesives, acrylic pressure-sensitive adhesives,vinyl alkyl ether pressure-sensitive adhesives, siliconepressure-sensitive adhesives, polyester pressure-sensitive adhesives,polyamide pressure-sensitive adhesives, urethane pressure-sensitiveadhesives, styrene-diene block copolymer pressure-sensitive adhesives,and creep-improved pressure-sensitive adhesives such as thesepressure-sensitive adhesives compounded with hot-melt resins havingmelting points of not more than approximately 200° C. These knownpressure-sensitive adhesives may be used singly or in combinations oftwo or more. The pressure-sensitive adhesive may be any known removablepressure-sensitive adhesive having removability such as those of solventtypes, emulsion types, and hot-melt types.

The removable pressure-sensitive adhesive typically used are rubberpressure-sensitive adhesives comprising natural rubber or a variety ofsynthetic rubbers as a base polymer; and acrylic pressure-sensitiveadhesives comprising a base polymer composed of an acrylic polymer(homopolymer or copolymer) in which one or two or more alkyl(meth)acrylates are used as monomer components. In the presentinvention, particularly acrylic pressure-sensitive adhesives comprisingan acrylic polymer as a base polymer are preferably used.

Examples of the alkyl (meth)acrylates used as the monomer component forthe acrylic polymer include C₁₋₂₀ alkyl (meth)acrylates such as methyl(meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl(meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl(meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl(meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate,2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, isodecyl(meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate,pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl(meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, andeicosyl (meth)acrylate.

To reform an aggregation force, heat resistance, and crosslinkability,the acrylic polymer may optionally include a unit corresponding to anadditional monomer component copolymerizable with the alkyl(meth)acrylate. Examples of such monomer components include(meth)acrylates having an aliphatic cyclic skeleton such as cyclopentyl(meth)acrylate, cyclohexyl (meth)acrylate, cyclohexylmethyl(meth)acrylate, and bornyl (meth)acrylate; (meth)acrylates having anaromatic carbon ring such as phenyl (meth)acrylate and benzyl(meth)acrylate; carboxyl group-containing monomers such as acrylic acid,methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate,itaconic acid, maleic acid, fumaric acid, and crotonic acid; acidanhydride group-containing monomers such as maleic anhydride anditaconic anhydride; hydroxyl group-containing monomers such ashydroxyethyl (meth) acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl(meth)acrylate, hydroxyhexyl (meth)acrylate, hydroxyoctyl(meth)acrylate, hydroxydecyl (meth)acrylate, hydroxylauryl(meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl methacrylate;sulfonate group-containing monomers such as styrene sulfonic acid, allylsulfonic acid, 2-(meth)acrylamide-2-methylpropanesulfonic acid,(meth)acrylamidepropanesulfonic acid, sulfopropyl (meth)acrylate, and(meth)acryloyloxynaphthalenesulfonic acid;(N-substituted)amide-containing monomers such as (meth)acrylamide,N,N-dimethyl(meth)acrylamide, N-butyl(meth)acrylamide,N-methylol(meth)acrylamide, and N-methylolpropane(meth)acrylamide;aminoalkyl (meth)acrylate monomers such as aminoethyl (meth)acrylate,N,N-dimethylaminoethyl (meth)acrylate, and t-butylaminoethyl(meth)acrylate; alkoxyalkyl (meth)acrylate monomers such as methoxyethyl(meth)acrylate and ethoxyethyl (meth)acrylate; maleimide monomers suchas N-cyclohexylmaleimide, N-isopropylmaleimide, N-laurylmaleimide, andN-phenylmaleimide; itaconimide monomers such as N-methylitaconimide,N-ethylitaconimide, N-butylitaconimide, N-octylitaconimide,N-2-ethylhexylitaconimide, N-cyclohexylitaconimide, andN-laurylitaconimide; succinimide monomers such asN-(meth)acryloyloxymethylenesuccinimide,N-(meth)acryloyl-6-oxyhexamethylenesuccinimide, andN-(meth)acryloyl-8-oxyoctamethylenesuccinimide; vinyl monomers such asvinyl acetate, vinyl propionate, N-vinylpyrrolidone,methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine,vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole,vinyloxazole, vinylmorpholine, N-vinylcarboxylic amides, styrene,α-methylstyrene, and N-vinylcaprolactam; cyano group-containing monomerssuch as acrylonitrile and methacrylonitrile; epoxy group-containingacrylic monomers such as glycidyl (meth)acrylate; glycol acrylic estermonomers such as polyethylene glycol (meth)acrylate, polypropyleneglycol (meth)acrylate, methoxyethylene glycol (meth)acrylate, andmethoxypolypropylene glycol (meth)acrylate; acrylic acid ester monomershaving a hetero ring, a halogen atom, a silicon atom, and the like suchas N-(meth)acryloylmorpholine, tetrahydrofurfuryl (meth)acrylate,fluorine (meth)acrylate, and silicone (meth)acrylate; polyfunctionalmonomers such as hexanediol di(meth)acrylate, (poly)ethylene glycoldi(meth)acrylate, (poly)propylene glycol di(meth)acrylate, neopentylglycol di(meth)acrylate, pentaerythritol di(meth)acrylate,trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate,dipentaerythritol hexa(meth)acrylate, epoxy acrylate, polyesteracrylate, and urethane acrylate; olefin monomers such as isoprene,butadiene, and isobutylene; and vinyl ether monomers such as vinylether. These monomer components may be used singly or in combinations oftwo or more.

The acrylic polymer can be prepared by a known radical polymerizationmethod such as solution polymerization, bulk polymerization, andemulsion polymerization. The acrylic polymer may be a random copolymer,a block copolymer, a graft polymer, or the like. In polymerization, apolymerization initiator and a chain transfer agent usually used can beused.

The base polymer for the pressure-sensitive adhesive has a weightaverage molecular weight of, for example, 10000 to 5000000, preferably20000 to 1000000. The base polymer having an excessively low weightaverage molecular weight readily contaminates an adherent with aresidual adhesive or the like after removal, for example, although sucha base polymer attains high followability to the adherent. The basepolymer having an excessively high weight average molecular weight willreduce followability to the adherent, although such a base polymerreduces contamination of the adherent with a residual adhesive or thelike after removal.

Besides the base polymer, the pressure-sensitive adhesive may optionallycontain proper additives such as a crosslinking agent (such as epoxycrosslinking agents, isocyanate crosslinking agents, melaminecrosslinking agents, oxazoline crosslinking agents, aziridinecrosslinking agents, and metal chelate compounds), a crosslinkingpromoter (crosslinking catalyst), a tackifier (such as rosin derivativeresins, polyterpene resins, petroleum resins, and oil-soluble phenolresins), a thickener, a plasticizer, a filler, a foaming agent, ananti-aging agent, an antioxidant, an ultraviolet absorbing agent, anantistatic agent, a surfactant, a leveling agent, a colorant, a flameretardant, and a silane coupling agent. In particular, to giveremovability to the pressure-sensitive adhesive, addition of acrosslinking agent is preferable.

The removable pressure-sensitive adhesive layer can be formed by a knownstandard method. Examples thereof include a method of applying apressure-sensitive adhesive composition onto a substrate (intermediatelayer when the intermediate layer is disposed on the substrate), and amethod of applying a pressure-sensitive adhesive composition onto aproper separator to form a pressure-sensitive adhesive layer, and thentransferring (adhering) the pressure-sensitive adhesive layer onto asubstrate (intermediate layer when the intermediate layer is disposed onthe substrate). Application can be performed with a coater, an extruder,or a printer typically used in formation of the pressure-sensitiveadhesive layer.

The removable pressure-sensitive adhesive layer has a thickness properlyselected according to applications or the like, which is, for example, 1to 100 μm, preferably approximately 1 to 50 μm.

The pressure-sensitive adhesiveness at 25° C. of the removablepressure-sensitive adhesive layer (peel by 180°, to a polyethyleneterephthalate film, tensile rate: 300 mm/min) may be within the rangeallowing removal, and is less than 3 N/20 mm, for example. The lowerlimit is approximately 0.01 N/20 mm, for example.

The protection film according to the present invention may optionallyinclude an additional layer (intermediate layer) between the substrateand the removable pressure-sensitive adhesive layer. On the removablepressure-sensitive adhesive layer, a separator for protecting theremovable pressure-sensitive adhesive layer may be disposed until theprotection film is used.

EXAMPLES

Hereinafter, the present invention will be more specifically describedusing Examples and Comparative Examples. The present invention will notbe limited to these. Evaluations in Examples and the like were made asfollows.

The following materials were used in Examples and the like.

<Polylactic Acid (A)>

A1: trade name “Terramac TP-4000” (made by Unitika Limited)

<Acidic Functional Group-Modified Olefin Polymer (B)>

B1: maleic anhydride group-containing modified polypropylene (weightaverage molecular weight: 32000, acid value: 52 mgKOH/g, trade name“Umex 1010,” made by Sanyo Chemical Industries, Ltd.)

<Fluorine-Containing Polymer (C)>

C1: acrylic-modified polytetrafluoroethylene (trade name “METABLENA-3000,” made by MITSUBISHI RAYON CO., LTD.)

<Crystallization Promoter (D)>

D1: zinc phenyl phosphonate (trade name “ECOPROMOTE,” made by NissanChemical Industries, Ltd.)

<Reforming Agent (E)>

E(a): polyglycerol fatty acid ester (number average molecular weight Mn:1300, trade name “Chirabasol VR-17,” made by Taiyo Kagaku Co., Ltd.)

E(b): core-shell-structured polymer (acrylic rubber/polymethylmethacrylate-styrene core-shell-structured polymer, trade name “PARALOIDEXL2315,” made by The Dow Chemical Company)

E(c): soft aliphatic polyester (polybutylene adipate terephthalate(trade name “Ecoflex,” made by BASF Japan Ltd.)

Examples 1 to 7

Each of resin compositions was prepared in the compounding proportionshown in Table 1 below, and was melt kneaded with a Banbury mixer. Bycalendering with a calender with four reverse-L shaped rolls, the resincomposition was formed into a film to have a thickness of 50 μm (meltfilm forming step). Next, as shown in FIG. 1, three rolls (take-offroll) heatable to any temperature were disposed immediately after themelt film forming step. The melt film formed resin composition waspassed through the three rolls in a staggered manner, and then throughcooling rolls to solidify the resin composition. A film was prepared.Subsequently, as shown in Table 1 below, the cooled and solidified andformed film was heated with a heat roll controlled to be anytemperature, thereby to promote crystallization (crystallizationpromoting step).

The temperature of the resin composition in the melt film forming step(“resin temperature in the melt film forming step”) was the surfacetemperature of a roll corresponding to the fourth roll 4 in FIG. 1. Thetemperature of the resin composition in the crystallization promotingstep (“crystallization promoting temperature”) was the surfacetemperature of the heat roll. The film forming rate was 5 m/min.

Comparative Examples 1 to 9

Each of resin compositions was prepared in the compounding proportionshown in Table 2 below in the same manner as in Examples except that thecrystallization promoting step was not performed, and was formed into afilm by calendering under film forming conditions shown in Table 2below.

The physical properties of the substrate were determined as follows.

<Melting Temperature (° C.)>

A temperature at the highest endothermic peak accompanied by melting ofthe resin composition after film formation during re-raising oftemperature was measured with a DSC (differential scanning calorimeter).The temperature was defined as a melting temperature (Tm; also referredto as a crystal melting peak temperature).

<Crystallization Temperature (° C.)>

A temperature at the highest exothermic peak accompanied bycrystallization of the resin composition after film formation during theraising of temperature from room temperature was measured with a DSC.The temperature was defined as a crystallization temperature (Tc;crystallization temperature during the raising of temperature, alsoreferred to as a crystallization peak temperature).

<Resin Temperature (° C.) in Melt Film Forming Step>

As above, in Examples and Comparative Examples, the surface temperatureof the fourth roll was measured, and was defined as the “resintemperature in the melt film forming step” (resin temperature in themelt film forming step).

<Residual Stress Relaxing Temperature (° C.)>

In this embodiment, a film sample was contacted with a take-off roll torelax residual stress. At this time, surface temperatures of threetake-off rolls in FIG. 1 (take-off roll temperatures) were approximatelythe same, and the temperatures were defined as a stress relaxingtemperature (° C.). The temperatures of the three take-off rolls may bedifferent if the temperatures fall within the temperature range.

<Crystallization Promoting Temperature (° C.)>

In this embodiment, the formed film was heated with a heat rollcontrolled to be any temperature, thereby to promote crystallization.The temperature of the heat roll was defined as a crystallizationpromoting temperature.

<Results of Film Forming Properties>

(1) Plate out to roll: dirt on the surface of the roll was visuallyevaluated, and was considered “o” (absent) if the surface of the rollhad no dirt and “x” (present) if the surface of the roll had dirt.(2) Peelability: peelability of the melt film formed resin compositionfrom the fourth roll 4 in FIG. 1 was evaluated, and was considered “o”(good) if the resin composition could be taken with the take-off roll 5,and “x” (poor) if the resin composition could not be taken with thetake-off roll 5.(3) State of film surface: the surface of the prepared film was visuallyobserved, and was considered “o” (good) if the film surface was smoothwithout roughness, and “x” (poor) if the surface of the film had bankmarks (depressions and projections caused by uneven flow of the resin),roughness, or pin holes.

<Tear Strength (N/Mm)>

Tear strength was measured according to JIS K7128-3: Plastics—Film andSheeting—Determination of Tear Resistance, Part 3: Right angled tearmethod. The following apparatus and conditions were used in themeasurement.

apparatus: tensile tester (Autograph AG-20kNG, manufactured by SHIMADZUCorporation)

sample size: shape of the test piece according to JIS

condition: tensile rate: 200 ram/min

The sample used for the evaluation was cut out such that the teardirection of the sample corresponded to the flow direction (hereinafterreferred to as MD) in film formation.

Method of calculating tear strength: Expression (3) below was used.

T=(F/d)  (3)

T: tear strength (N/mm)

F: the largest tensile load (N)

d: thickness of the test piece (mm)

<Amount of Crystallization Heat ΔHc′ (J/g) after Film Formation>

The amount of heat ΔHc (J/g) at the exothermic peak accompanied bycrystallization of the film sample after film formation during theraising of temperature, and the amount of heat ΔHm (J/g) accompanied bymelting when the temperature was raised to 200° C., was lowered to 0°C., and was then raised again were measured with a DSC. From the ΔHc(J/g) and the ΔHm (J/g), ΔHc′ was calculated using Expression (5) belowwhere ΔHc′ was the amount of crystallization heat after film formation(amount of melt endotherm in crystallized portions during filmformation).

ΔHc′=ΔHm−ΔHc  (5)

The following DSC was used in the measurements of the crystallizationtemperature, the melting temperature, a relative crystallization rate,and the amount of crystallization heat ΔHc′ after film formation:

apparatus: DSC6220 manufactured by SII NanoTechnology Inc.

The measurement conditions are:

range of temperature in the measurement: 20° C. to 200° C. to 0° C. to200° C. (namely, first, the measurement during the raising oftemperature from 20° C. to 200° C., followed by the measurement duringlowering of temperature from 200° C. to 0° C., finally followed by themeasurement during re-raising of temperature from 0° C. to 200° C.)

temperature raising/falling rate: 2° C./rain

atmosphere for the measurement: under a nitrogen atmosphere (200 ml/min)

No exothermic peak accompanied by crystallization was found during there-raising of temperature. From this, it was determined that 100% ofcrystallizable regions was crystallized at the temperature falling rateof 2° C./rain, and adequacy of the calculation expression for the amountof crystallization heat after film formation was confirmed.

<Rate of Dimensional Change Due to Heating>

A film measuring 100 mm×100 mm was cut out, was marked with a gauge lineat 50 mm in the flow direction (hereinafter referred to as MD) and thetransverse direction (hereinafter referred to as TD) during filmformation. The film was placed in an oven heated to 120° C. for 1minute, and was examined for the dimensional change after the film wasextracted.

Method of calculating a rate of dimensional change due to heating; thegauge length L1 before a test and the gauge length L2 after the testwere measured, and the rate of dimensional change due to heating wascalculated from Expression (1):

rate of dimensional change due to heating (%)=(L2 −L1)/L1×100  (1)

(Evaluation) The dimensional change rates by heating of not more than±3% in MD and TD are accepted.

<Rate of Dimensional Change Due to Loaded Heating>

A film measuring 100 mm (MD)×20 mm (TD) was cut out, and was marked witha gauge line at 50 mm in MD. While a load of 300 g/mm² was being appliedin MD, the film was placed in an oven heated to 100° C. for 1 minute.The dimensional change in MD of the film was examined after the film wasextracted.

Method of calculating a rate of dimensional change due to loadedheating; the gauge length L3 before a test and the gauge length L4 afterthe test were measured, and the rate of dimensional change due to loadedheating was calculated from Expression (2):

rate of dimensional change due to heating (%)=(L4 −L3)/L3×100  (2)

(Evaluation) The rate of dimensional change due to loaded heating of notmore than ±3% is accepted.

This evaluation was performed as an alternative evaluation inconsideration of a drying step during actual application of thepressure-sensitive adhesive on the premise that the film was wound intoa roll while a certain tension was being applied to the film.

Results of evaluation in Examples 1 to 7 and Comparative Examples 1 to 9are shown in Tables 1 and 2 below. In Example 1 and Comparative Examples1 to 3 where the reforming agent is not added, Example 1 showed hightear resistance and high heat resistance. In contrast, ComparativeExample 1, which includes no crystallization step, shows high tearresistance. Unfortunately, the film in Comparative Example 1 cannotendure heat load deformation due to its low amount of crystallizationheat. Comparative Example 2 shows poor tear resistance although highheat resistance is attained by crystallization during film formation.Comparative Example 3 shows poor tear resistance and poor heatresistance because the residual stress is not relaxed due to a lowtemperature of the take-off roll.

In Examples 2 and 3 and Comparative Examples 4 and 5 where the reformingagent E(a) is added, Examples 2 and 3 showed high tear resistance andhigh heat resistance. Examples 2 and 3 have tear strength greater thanthat in Example 1 where the reforming agent is not added, and show theeffect of compounding the reforming agent. In contrast, ComparativeExample 4, which includes no crystallization step, shows high tearresistance. Unfortunately, the film in Comparative Example 4 cannotendure heat load deformation due to its low amount of crystallizationheat. Comparative Example 3 shows poor tear resistance although highheat resistance is attained by crystallization during film formation.

In Examples 4 and 5 and Comparative Examples 6 and 7 where the reformingagent E(b) is added, Examples 4 and 5 showed high tear resistance andhigh heat resistance. Examples 4 and 5 have tear strength greater thanthat in Example 1 where the reforming agent is not added, and show theeffect of compounding the reforming agent. In contrast, ComparativeExample 6, which includes no crystallization step, shows high tearresistance. Unfortunately, the film in Comparative Example 6 cannotendure heat load deformation due to its low amount of crystallizationheat. Comparative Example 5 shows poor tear resistance although highheat resistance is attained by crystallization during film formation.

In Examples 6 and 7 and Comparative Examples 8 and 9 where the reformingagent E(c) is added, Examples 6 and 7 showed high tear resistance andhigh heat resistance. Examples 6 and 7 have tear strength greater thanthat in Example 1 where the reforming agent is not added, and show theeffect of compounding the reforming agent. In contrast, ComparativeExample 8, which includes no crystallization step, shows high tearresistance. Unfortunately, the film in Comparative Example 8 cannotendure heat load deformation due to its low amount of crystallizationheat. Comparative Example 7 shows poor tear resistance although highheat resistance is attained by crystallization during film formation.

TABLE 1 Example 1 2 3 4 5 6 7 Raw materials (parts by weight) A1 100 9791 90 85 90 70 B1 1 1 1 1 1 1 1 C1 3 1 3 3 3 3 6 D1 1 1 1 1 1 1 1 E (a)3 9 1 1 E (b) 10 15 E (c) 10 30 Film thickness (μm) 50 50 50 50 50 50 50DSC data on resin Melting temperature 172 165 165 167 167 167 167composition Crystallization temperature (Tc) 87 84 84 83 83 85 85Setting Resin temperature in melt film forming 162 162 170 162 162 162162 temperature (° C.) step Residual stress relaxing temperature 142 120142 110 142 110 142 Crystallization promoting temperature 120 120 120120 110 120 110 Crystallization promoting time (seconds) 30 60 30 60 3060 60 Results of film Plate out to roll ∘ ∘ ∘ ∘ ∘ ∘ ∘ formingPeelability ∘ ∘ ∘ ∘ ∘ ∘ ∘ properties State of film surface ∘ ∘ ∘ ∘ ∘ ∘ ∘Tear strength (N/mm) MD 110 136 152 152 176 141 191 Amount ofcrystallization heat after film formation ΔHc′ 34 36 30 33 29 29 25(J/g) Rate of dimensional change MD 0.2 0.0 −1.0 0.0 −0.2 −0.3 0.1 dueto heating (%) TD −0.2 −0.1 −0.5 −0.1 −0.3 0.0 −0.1 Rate of dimensionalchange MD 2.0 0.0 0.0 2.0 1.0 1.2 2.8 due to loaded heating (%)

TABLE 2 Comparative Example 1 2 3 4 5 6 7 8 9 Raw materials (parts byweight) A1 100 100 100 97 94 94 90 85 85 B1 1 1 1 1 1 1 1 1 1 C1 3 3 5 63 2 3 4 4 D1 1 1 1 1 1 1 1 1 1 E (a) 3 6 1 1 E (b) 6 10 E (c) 15 15 Filmthickness (μm) 50 50 50 50 50 50 50 50 50 DSC data on Meltingtemperature 172 172 172 165 165 167 167 167 167 resin Crystallizationtemperature (Tc) 87 87 87 84 84 83 83 85 85 composition Setting Resintemperature in melt film forming 162 152 152 148 168 150 162 150 162temperature step (° C.) Residual stress relaxing temperature 142 142 90120 110 120 110 120 110 Crystallization promoting temperature — — — — —— — — — Crystallization promoting time (seconds) — — — — — — — — —Results of Plate out to roll ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ film forming Peelability∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ properties State of film surface ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘Tear strength (N/mm) MD 259 34 32 54 245 82 275 88 283 Amount ofcrystallization heat after film formation 18 32 35 37 17 38 17 27 15ΔHc′ (J/g) Rate of dimensional change MD −4.1 −1.3 −4.3 −1.2 −8.0 −1.8−6.2 −1.7 −1.2 due to heating (%) TD −1.4 −0.1 0.5 0.1 −0.5 0.3 0.1 −0.1−0.6 Rate of dimensional change MD ND* −1.0 −5.2 −1.5 ND* −1.0 ND* −1.0ND* due to loaded heating (%) *cannot be measured because the sample iscompletely elongated by load

INDUSTRIAL APPLICABILITY

The substrate in the protection film according to the present inventiondoes not melt or deform at high temperatures more than 100° C. Thesubstrate keeps its intrinsic rigidity and does not break or tear whentension is applied during, for example, production or processing of theprotection film or winding thereof into a roll. Furthermore, thesubstrate in the protection film according to the present invention doesnot break or tear when the protection film is re-attached in use or isfinally peeled. Consequently, the protection film is particularlyuseful, for example, as a protection film for protecting the surfaces ofwheels of vehicles; as a protection film for protecting the surfaces ofoptical members and electronic parts used in liquid crystal displays andthe like such as polarizing plates, wavelength plates, retardationplates, and reflective sheets; and as a protection film for protectingthe surfaces of metallic layers or metal oxide layers used inelectromagnetic wave shielding materials and the like used in plasmadisplay panels and CRTs.

REFERENCE SIGNS LIST

-   -   1 first roll    -   2 second roll    -   3 third roll    -   4 fourth roll    -   5 take-off roll    -   6 cooling roll    -   7 cooling roll    -   8 resin composition    -   9 bank (resin pool)    -   10 tip of extruder

1. A protection film comprising a substrate and a removablepressure-sensitive adhesive layer on at least one surface of thesubstrate, wherein the substrate is composed of a polylactic acid filmor sheet comprising polylactic acid (A), wherein a tear strength(according to JIS K7128-3: Plastics—Film and Sheeting—Determination ofTear Resistance, Part 3: Right angled tear method) of the film or sheetis not less than 100 N/mm when the film or sheet is torn at least in aflow direction (machine direction: MD), the film or sheet stored underan atmosphere at 100° C. for 1 minute has a rate of dimensional changedue to heating of not more than ±3% in the flow direction (MD) and atransverse direction (TD), the rate of dimensional change due to heatingbeing determined by Expression (1):rate of dimensional change due to heating (%)=(L2−L1)/L1×100  (1) whereL1 represents a gauge length before a test, and L2 represents a gaugelength after the test, and the film or sheet stored under an atmosphereat 100° C. for 1 minute while a load of 300 g/mm² is applied in the flowdirection (MD) has a rate of dimensional change due to loaded heating ofnot more than ±3% in the flow direction (MD), the rate of dimensionalchange due to loaded heating being determined by Expression (2):rate of dimensional change due to loaded heating (%)=(L4−L3)/L3×100  (2)where L3 represents a gauge length before a test, and L4 represents agauge length after the test.
 2. The protection film according to claim1, wherein the polylactic acid film or sheet included in the substratefurther comprises a reforming agent (E).
 3. The protection filmaccording to claim 2, wherein the polylactic acid film or sheet includedin the substrate comprises polyglycerol fatty acid ester and/orpolyglycerol condensed hydroxy fatty acid ester (a) as the reformingagent (E) such that the weight ratio of the polylactic acid (A) to thepolyglycerol fatty acid ester and/or polyglycerol condensed hydroxyfatty acid ester (a) is 99:1 to 80:20 ((A):total amount of (a)).
 4. Theprotection film according to claim 2, wherein the polylactic acid filmor sheet included in the substrate comprises a core-shell-structuredpolymer (b) composed of a particulate rubber and a graft layer formed onthe outside of the rubber as the reforming agent (E) such that theweight ratio of the polylactic acid (A) to the core-shell-structuredpolymer (b) composed of a particulate rubber and a graft layer formed onthe outside of the rubber is 99:1 to 80:20 ((A):(b)).
 5. The protectionfilm according to claim 2, wherein the polylactic acid film or sheetincluded in the substrate comprises a soft aliphatic polyester (c) asthe reforming agent (E) such that the weight ratio of the polylacticacid (A) to the soft aliphatic polyester (c) is 95:5 to 60:40 ((A):(c)).6. The protection film according to claim 1, wherein the polylactic acidfilm or sheet included in the substrate further comprises 0.1 to 10parts by weight of an acidic functional group-modified olefin polymer(B) based on 100 parts by weight of the polylactic acid (A) (or acomposition comprising the polylactic acid (A) and the reforming agent(E) when the reforming agent (E) is contained), the acidic functionalgroup-modified olefin polymer (B) having an acid value of 10 to 70mgKOH/g and a weight average molecular weight of 10000 to
 80000. 7. Theprotection film according to claim 6, wherein the acidic functionalgroup of the acidic functional group-modified olefin polymer (B) is anacid anhydride group.
 8. The protection film according to claim 1,wherein the polylactic acid film or sheet included in the substratefurther comprises 0.5 to 15 parts by weight of a fluorine-containingpolymer (C) based on 100 parts by weight of the polylactic acid (A) (ora composition comprising the polylactic acid (A) and the reforming agent(E) when the reforming agent (E) is contained).
 9. The protection filmaccording to claim 8, wherein the fluorine-containing polymer (C) is atetrafluoroethylene polymer.
 10. The protection film according to claim1, wherein the polylactic acid film or sheet included in the substratefurther comprises 0.1 to 15 parts by weight of a crystallizationpromoter (D) based on 100 parts by weight of the polylactic acid (A) (ora composition comprising the polylactic acid (A) and the reforming agent(E) when the reforming agent (E) is contained).
 11. The protection filmaccording to claim 1, wherein the polylactic acid film or sheet includedin the substrate is a film or sheet formed by a melt film formingmethod.
 12. The protection film according to claim 11, wherein the meltfilm forming method is calendering.
 13. A method of producing aprotection film comprising a substrate composed of a polylactic acidfilm or sheet prepared by fanning a resin composition comprisingpolylactic acid (A) into a film by a melt film forming method, themethod comprising: a melt film forming step of melt forming the resincomposition, a cooling solidifying step of cooling and solidifying theresin composition after the melt film forming step to prepare a film orsheet, and a crystallization promoting step of heating the film or sheetafter the cooling solidifying step to promote crystallization of thefilm or sheet, wherein a resin temperature in the melt film forming stepis within the range of (Tm) −15° C. to (Tm) +15° C. where Tm representsa melting temperature of the resin composition during raising oftemperature, and in at least part of the crystallization promoting step,crystallization of the film or sheet is promoted within the temperaturerange of (Tc) +10° C. to (Tc) +50° C. where Tc represents acrystallization temperature of the resin composition during the raisingof temperature.
 14. The method of producing a protection film accordingto claim 13, further comprising a residual stress relaxing step afterthe melt film forming step and before the cooling solidifying step,wherein in the residual stress relaxing step, the resin composition iskept within the temperature range of (Tm) −70° C. to (Tm) 20° C.
 15. Themethod of producing a protection film according to claim 13, wherein theresin composition further comprises a reforming agent (E).
 16. Themethod of producing a protection film according to claim 15, wherein theresin composition comprises polyglycerol fatty acid ester and/orpolyglycerol condensed hydroxy fatty acid ester (a) as the reformingagent (E) such that the weight ratio of the polylactic acid (A) to thepolyglycerol fatty acid ester and/or polyglycerol condensed hydroxyfatty acid ester (a) is 99:1 to 80:20 ((A):total amount of (a)).
 17. Themethod of producing a protection film according to claim 15, wherein theresin composition comprises a core-shell-structured polymer (b) composedof a particulate rubber and a graft layer formed on the outside of therubber as the reforming agent (E) such that the weight ratio of thepolylactic acid (A) to the core-shell-structured polymer (b) composed ofa particulate rubber and a graft layer formed on the outside of therubber is 99:1 to 80:20 ((A):(b)).
 18. The method of producing aprotection film according to claim 15, wherein the resin compositioncomprises a soft aliphatic polyester (c) as the reforming agent (E) suchthat the weight ratio of the polylactic acid (A) to the soft aliphaticpolyester (c) is 95:5 to 60:40 ((A):(c)).
 19. The method of producing aprotection film according to claim 13, wherein the resin compositionfurther comprises 0.1 to 10 parts by weight of an acidic functionalgroup-modified olefin polymer (B) based on 100 parts by weight of thepolylactic acid (A) (or a composition comprising the polylactic acid (A)and the reforming agent (E) when the reforming agent (E) is contained),the acidic functional group-modified olefin polymer (B) having an acidvalue of 10 to 70 mgKOH/g and a weight average molecular weight of 10000to
 80000. 20. The method of producing a protection film according toclaim 19, wherein the acidic functional group of the acidic functionalgroup-modified olefin polymer (B) is an acid anhydride group.
 21. Themethod of producing a protection film according to claim 13, wherein theresin composition further comprises 0.5 to 15 parts by weight of afluorine-containing polymer (C) based on 100 parts by weight of thepolylactic acid (A) (or a composition comprising the polylactic acid (A)and the reforming agent (E) when the reforming agent (E) is contained).22. The method of producing a protection film according to claim 21,wherein the fluorine-containing polymer (C) is a tetrafluoroethylenepolymer.
 23. The method of producing a protection film according toclaim 13, wherein the resin composition further comprises 0.1 to 15parts by weight of a crystallization promoter (D) based on 100 parts byweight of the polylactic acid (A) (or a composition comprising thepolylactic acid (A) and the reforming agent (E) when the reforming agent(E) is contained).
 24. The method of producing a protection filmaccording to claim 13, wherein the melt film forming method iscalendering.